Metal-gate CMOS device and fabrication method thereof

ABSTRACT

A method for fabricating a metal-gate CMOS device. A substrate having thereon a first region and a second region is provided. A first dummy gate structure and a second dummy gate structure are formed within the first region and the second region respectively. A first LDD is formed on either side of the first dummy gate structure and a second LDD is formed on either side of the second dummy gate structure. A first spacer is formed on a sidewall of the first dummy gate structure and a second spacer is formed on a sidewall of the second dummy gate structure. A first embedded epitaxial layer is then formed in the substrate adjacent to the first dummy gate structure. The first region is masked with a seal layer. Thereafter, a second embedded epitaxial layer is formed in the substrate adjacent to the second dummy gate structure.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application is a divisional application of and claims priority to U.S. patent application Ser. No. 13/070,483, filed on Mar. 24, 2011, and entitled “metal-gate CMOS device” the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to semiconductor device and fabrication method thereof. More particularly, the present invention relates to a dual work-function metal-gate CMOS device and fabrication method thereof.

2. Description of the Prior Art

The continued scaling of CMOS devices into sub-40 nm technology will rely on a fundamental change in transistor gate stack materials. Over the past few years, research in this area has focused on identifying candidate materials to replace polysilicon and SiO₂ as the gate electrode and gate dielectric, respectively. Critical requirements for novel gate electrode materials include thermal stability with the gate dielectric and suitable values for the interfacial work function. The latter requirement of obtaining complementary gate work functions on a single wafer is being perceived as a major process integration challenge.

Metal-gate electrodes bring about several advantages compared to traditional polysilicon gates as CMOS technology continues to scale beyond the 40 nm node. These include reduction in poly-depletion effect, reduction in sheet resistance, and potentially better thermal stability on high-K gate dielectrics. The main challenge is that, unlike with polysilicon, one would have to use two metallic materials (bi-layer metal) with different work functions in order to achieve the right threshold voltages for both NMOS and PMOS.

The conventional dual metal gate methods are categorized into the gate-first process and the gate-last process. Among the two main approaches, the gate-last process is able to avoid processes of high thermal budget and to provide wider material choices for the high-K gate dielectric layer and the metal gate, and thus gradually replaces the gate-first process. In a conventional gate-last process, a dummy gate (or “replacement gate”) is formed on a substrate and followed by steps of forming a conventional MOS transistor and forming an inter-layer dielectric (ILD) layer. Subsequently, the dummy gate is removed to form a gate trench. Thereafter, the gate trench is filled with metal layers required for different conductivity types.

It is well known in the art that the degree of difficulty for fabricating a well-controlled double work function metal is immense as the process often involves complicated integration between NMOS device and PMOS device. The difficulty increases even more as the thickness and materials used in double work function metal gates requires a much more strict demand. Hence, how to successfully integrate the fabrication of a conventional double work function metal gate transistor so as to reduce its complexity to the standard CMOS process flow has become an important study in the field.

SUMMARY OF THE INVENTION

It is one objective of the invention to provide an improved method for fabricating a dual work-function metal-gate CMOS device, which integrates embedded SiGe/SiC epitaxial processes and is capable of simplifying the CMOS fabrication steps and complexity, thereby reducing manufacture cost.

According to one aspect of the invention, a method for fabricating a metal-gate CMOS device is provided. A substrate having thereon a first region and a second region is provided. A first dummy gate structure and a second dummy gate structure are formed within the first region and the second region respectively. A first lightly doped drain (LDD) is formed on either side of the first dummy gate structure and a second LDD is formed on either side of the second dummy gate structure. A first spacer is formed on a sidewall of the first dummy gate structure and a second spacer is formed on a sidewall of the second dummy gate structure. A first embedded epitaxial layer is then formed in the substrate adjacent to the first dummy gate structure. The first region is masked with a seal layer. Thereafter, a second embedded epitaxial layer is formed in the substrate adjacent to the second dummy gate structure.

After forming the second embedded epitaxial layer, a first contact hole etch stop layer (CESL) on the substrate is deposited in a blanket manner to cover the first and second regions. A first dielectric layer is then formed on the first CESL. A chemical mechanical polishing (CMP) process is performed to remove a portion of the first dielectric layer and a portion of the first CESL to expose the first and second dummy gate structures. The first and second dummy gate structures is then removed to thereby form a first gate trench and a second gate trench. A first gate dielectric layer and a first metal gate are formed in the first gate trench. A second dielectric layer and a second metal gate are formed in the second gate trench.

After forming the first and second metal gates, a second dielectric layer is formed on the substrate. The first and second dielectric layers, the first CESL and the seal layer in the first region are etched to form a first contact hole, and the first and second dielectric layers and the first CESL in the second region are etched to form a second contact hole. A silicide layer is then formed at a bottom of each of the first and second contact holes. The first and second contact holes are filled with a metal layer to thereby form a first contact plug and a second contact plug.

According to another embodiment of the invention, after forming the second embedded epitaxial layer, the first dielectric layer, the first CESL and the seal layer are removed. A stressed second CESL is deposited. A third dielectric layer is then deposited on the stressed second CESL. The third dielectric layer and the stressed second CESL in the first region are etched to form a first contact hole, and the third dielectric layer and the stressed second CESL in the second region are etched to form a second contact hole. A silicide layer is formed at a bottom of each of the first and second contact holes. The first and second contact holes are filled with a metal layer to thereby form a first contact plug and a second contact plug.

In one aspect, the present invention provides a metal-gate CMOS device including a substrate having a PMOS region and an NMOS region; a PMOS transistor in the PMOS region of the substrate; an NMOS transistor in the NMOS region of the substrate; a seal layer only masking the PMOS transistor within the PMOS region; and a contact hole etch stop layer (CESL) covering the seal layer within the PMOS region and covering the NMOS transistor within the NMOS region. The PMOS transistor comprises a first metal gate and a first gate dielectric layer. The first gate dielectric layer comprises metal oxide including hafnium oxide (HfO₂), hafnium silicon oxide (HfSiO₄), hafnium silicon oxynitride (HfSiON), aluminum oxide (Al₂O₃), lanthanum oxide (La₂O₃), lanthanum aluminum oxide (LaAlO₃), tantalum oxide (Ta₂O₅), zirconium oxide (ZrO₂), zirconium silicon oxide (ZrSiO₄), or hafnium zirconium oxide (HfZrO₂). The PMOS transistor further comprises an embedded SiGe epitaxial layer in a source/drain region of the PMOS transistor and an embedded SiC epitaxial layer in a source/drain region of the NMOS transistor.

These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 to FIG. 14 are schematic, cross-sectional diagrams showing a method for fabricating a dual work-function CMOS device in accordance with one preferred embodiment of this invention.

FIG. 15 to FIG. 16 are schematic, cross-sectional diagrams showing a method for fabricating a dual work-function CMOS device in accordance with another preferred embodiment of this invention.

DETAILED DESCRIPTION

Please refer to FIG. 1 to FIG. 14. FIG. 1 to FIG. 14 are schematic, cross-sectional diagrams showing a method for fabricating a dual work-function CMOS device in accordance with one preferred embodiment of this invention. As shown in FIG. 1, a substrate 10 such as silicon substrate, silicon-containing substrate, silicon-on-insulator (SOI) substrate or epitaxial substrate is provided. A plurality of shallow trench isolation (STI) structures 12 are provided in the main surface of the substrate 10 to electrically isolate at least one PMOS region 101 and at least one NMOS region 102. Subsequently, a dummy gate structure 21 and a dummy gate structure 22 are formed on the substrate 10 within the PMOS region 101 and the NMOS region 102 respectively. The dummy gate structure 21 may comprise a gate oxide layer 21 a, a polysilicon layer 21 b, a cap layer 21 c and a sidewall oxide layer 21 d. The dummy gate structure 22 may comprise a gate oxide layer 22 a, a polysilicon layer 22 b, a cap layer 22 c and a sidewall oxide layer 22 d. The cap layer 21 c or the cap layer 22 c may comprise silicon nitride. After the formation of the dummy gate structures 21 and 22, a patterned photoresist layer 30 is used to mask the PMOS region 101. The NMOS region 102 is exposed by the opening 30 a in the patterned photoresist layer 30. An LDD ion implantation 130 is carried out to form LDD regions 220 in the substrate 10 next to the dummy gate structure 22 within the NMOS region 102.

As shown in FIG. 2, after the LDD ion implantation 130, the patterned photoresist layer 30 is stripped off. Another patterned photoresist layer 40 is used to mask the NMOS region 102. The PMOS region 101 is exposed by the opening 40 a in the patterned photoresist layer 40. An LDD ion implantation 140 is then carried out to form LDD regions 210 in the substrate 10 next to the dummy gate structure 21 within the PMOS region 101. Thereafter, the patterned photoresist layer 40 is stripped off. Of course, it is to be understood that the LDD step in FIG. 1 and the LDD step in FIG. 2 are interchangeable. For example, the LDD regions 210 in the PMOS region 101 may be formed prior to the formation of the LDD regions 220 in the NMOS region 102.

As shown in FIG. 3, a spacer material layer 50 is deposited over the substrate 10 in a blanket manner. The spacer material layer 50 covers the PMOS region 101 and the NMOS region 102. According to the preferred embodiment of the invention, the spacer material layer 50 is carbon-doped silicon nitride layer with its dielectric constant that is higher than the dielectric constant of the undoped silicon nitride. As shown in FIG. 4, subsequently, an anisotropic dry etching process is performed to etch the spacer material layer to thereby form a pair of spacers 51 on the sidewalls of the dummy gate structure 21 and a pair of spacers 52 on the sidewalls of the dummy gate structure 22. It is noteworthy that one technical feature of this invention is that the gate sidewall spacers are formed after the LDD implant.

Subsequently, as shown in FIG. 5, a sacrificial silicon nitride layer 54 is deposited over the substrate 10 in a blanket manner. The sacrificial silicon nitride layer 54 covers the PMOS region 101 and the NMOS region 102. According to the preferred embodiment of this invention, the sacrificial silicon nitride layer 54 may be undoped silicon nitride layer as long as significant etching selectivity is present between the spacer material layer 50 and the sacrificial silicon nitride layer 54. More specifically, the etching rate of the sacrificial silicon nitride layer 54 is much higher than the etching rate of the spacer material layer 50.

As shown in FIG. 6, a patterned photoresist layer 60 is used to mask the NMOS region 102. The PMOS region 101 is exposed by the opening 60 a in the patterned photoresist layer 60. Subsequently, a self-aligned etching process is performed to form a sigma-shaped recess 71 in the substrate 10 on each side of the dummy gate structure 21 within the PMOS region 101. After the formation of the sigma-shaped recess 71, the patterned photoresist layer 60 is stripped off. As shown in FIG. 7, a SiGe epitaxial process is carried out in the PMOS region 101 to grow SiGe epitaxial layer 81 in the sigma-shaped recess 71. According to the preferred embodiment of this invention, the SiGe epitaxial layer 81 is in-situ doped with P type dopants to thereby form a P⁺ embedded SiGe epitaxial layer 81. By doing so, the subsequent source/drain (S/D) ion implantation step for the PMOS and the corresponding P⁺ S/D photo mask can be spared.

As shown in FIG. 8, an etching process is performed to selectively remove the remaining sacrificial silicon nitride layer 54 from the NMOS region 102. In other embodiments, however, this etching process may be omitted. Subsequently, a deposition process is performed, for example, a chemical vapor deposition (CVD) process or an atomic layer deposition (ALD) process, to deposit a silicon nitride seal layer 56 over the substrate 10 in a blanket manner. The silicon nitride seal layer 56 may have a thickness of about 50-200 angstroms.

As shown in FIG. 9, a patterned photoresist layer 80 is used to mask the PMOS region 101. The NMOS region 102 is exposed by the opening 80 a in the patterned photoresist layer 80. Subsequently, an etching process is performed to form a sigma-shaped recess 72 in the substrate 10 on each side of the dummy gate structure 22 within the NMOS region 102. After the formation of the sigma-shaped recess 72, the patterned photoresist layer 80 is stripped off. As shown in FIG. 10, a SiC epitaxial process is carried out in the NMOS region 102 to grow SiC epitaxial layer 82 in the sigma-shaped recess 72. According to the preferred embodiment of this invention, the SiC epitaxial layer 82 is in-situ doped with N type dopants to thereby form an N⁺ embedded SiC epitaxial layer 82. By doing so, the subsequent source/drain (S/D) ion implantation step for the NMOS and the corresponding N⁺ S/D photo mask can be spared. It is understood that the embedded SiGe epitaxial steps for PMOS region in FIGS. 6-7 and the embedded SiC epitaxial for NMOS region in FIGS. 9-10 are interchangeable. For example, the embedded SiC epitaxial for NMOS region may be carried out prior to the embedded SiGe epitaxial steps for PMOS region in other cases.

As shown in FIG. 11, a contact hole etch stop layer (CESL) 90 such as a silicon nitride layer is deposited over the substrate 10 in a blanket manner. The CESL 90 may have a thickness of about 100-150 angstroms. According to the preferred embodiment of this invention, the CESL 90 does not contain stress. Subsequently, a dielectric layer 91 such as silicon oxide or low-k material is deposited onto the CESL 90.

As shown in FIG. 12, an upper portion of the dielectric layer 91, a portion of the CESL 90, the cap layer 21 c of the dummy gate structure 21 and the cap layer 22 c of the dummy gate structure 22 are removed by CMP (chemical mechanical polishing), thereby exposing the polysilicon layer 21 b of the dummy gate structure 21 and the polysilicon layer 22 b of the dummy gate structure 22. Subsequently, the remaining dummy gate structure 21 including the polysilicon layer 21 b and the gate oxide layer 21 a and the remaining dummy gate structure 22 including the polysilicon layer 22 b and the gate oxide layer 22 a are completely removed by etching methods, thereby forming gate trench 321 and gate trench 322, which expose the PMOS channel region 121 and the NMOS channel region 122 respectively.

As shown in FIG. 13, a high-k gate dielectric layer 421 a and a metal gate 421 b are formed inside the gate trench 321, and a high-k gate dielectric layer 422 a and a metal gate 422 b are formed inside the gate trench 322. According to the preferred embodiment of this invention, the high-k gate dielectric layers 421 a and 422 a may include but not limited to silicon nitride, silicon oxynitride or metal oxide. For example, the aforesaid metal oxide may include but not limited to hafnium oxide (HfO₂), hafnium silicon oxide (HfSiO₄), hafnium silicon oxynitride (HfSiON), aluminum oxide (Al₂O₃), lanthanum oxide (La₂O₃), lanthanum aluminum oxide (LaAlO₃), tantalum oxide (Ta₂O₅), zirconium oxide (ZrO₂), zirconium silicon oxide (ZrSiO₄), or hafnium zirconium oxide (HfZrO₂). The metal gates 422 a and 422 b may include but not limited to titanium nitride, aluminum nitride, tantalum nitride, aluminum or work-function metals. The metal gates 421 b and 422 b may be single-layered or composite layer. The high-k gate dielectric layers 421 a and 422 a may be formed by CVD methods or ALD methods, for example. The metal gates 421 b and 422 b may be formed by CVD methods, PVD methods or sputtering methods. The excess metal layers outside the gate trenches 321 and 322 may be removed by CMP.

As shown in FIG. 14, after the high-k/metal gate (HK/MG) processes, a dielectric layer 92 may be deposited over the substrate in a blanket manner. Subsequently, a contact hole/contact plug forming process is carried out. A dry etching process is performed to etch the dielectric layers 92 and 91, the CESL 90 and the silicon nitride seal layer 56 within the PMOS region 101 to form the contact holes 92 a exposing source/drain regions of the PMOS transistor, and etch the dielectric layers 92 and 91, and the CESL 90 within the NMOS region 102 to form the contact holes 92 b exposing the source/drain regions of the NMOS transistor. Thereafter, a self-aligned silicidation process is performed to form salicide layers 171 and 172 such as nickel silicide (NiSi) or NiPt at the bottom of the contact hole 92 a and the bottom of the contact hole 92 b respectively. Thereafter, metal adhesion layer such as titanium, titanium nitride or tungsten is deposited to fill the contact holes 92 a and 92 b thereby forming contact plugs 192 a and 192 b. As can be seen in FIG. 14, one of the technical features of the invention is that the PMOS region 101 is covered by silicon nitride seal layer 56 and the CESL 90 while the NMOS region 102 is covered by CESL 90.

FIG. 15 to FIG. 16 demonstrate an alternative method for fabricating the dual work-function metal-gate CMOS device in accordance with another embodiment of this invention, wherein FIG. 15 follows the step as shown in FIG. 13. As shown in FIG. 15, after the HK/MG process as set forth in FIG. 13, the remaining dielectric layer 91, the CESL 90 and the silicon nitride seal layer 56 are removed. Another CESL 93 and another dielectric layer 94 are deposited onto the substrate 10. According to the preferred embodiment of this invention, the CESL 93 is a stressed CESL, for example, tensile-stressed or compressive-stressed. The stressed CESL 93 is used to improve the device performance.

Subsequently, as shown in FIG. 16, a contact hole/contact plug forming process is carried out. A dry etching process is performed to etch the dielectric layers 94 and the CESL 93 within the PMOS region 101 to form the contact holes 94 a exposing source/drain regions of the PMOS transistor, and etch the dielectric layers 94 and the CESL 93 within the NMOS region 102 to form the contact holes 94 b exposing the source/drain regions of the NMOS transistor. A self-aligned silicidation process is then performed to form salicide layers 271 and 272 such as nickel silicide at the bottom of the contact hole 94 a and the bottom of the contact hole 94 b respectively. Thereafter, metal adhesion layer such as titanium, titanium nitride or tungsten is deposited to fill the contact holes 94 a and 94 b thereby forming contact plugs 194 a and 194 b.

Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims. 

What is claimed is:
 1. A method for fabricating a metal-gate CMOS device, comprising: providing a substrate having thereon a first region and a second region; forming a first dummy gate structure and a second dummy gate structure within the first region and the second region respectively; forming a first lightly doped drain (LDD) on either side of the first dummy gate structure and a second LDD on either side of the second dummy gate structure; forming a first spacer on a sidewall of the first dummy gate structure and a second spacer on a sidewall of the second dummy gate structure; forming a first embedded epitaxial layer in the substrate adjacent to the first dummy gate structure; masking the first region with a seal layer; forming a first contact hole etch stop layer (CESL) covering the seal layer within the first region and covering the second region, wherein the first CESL does not contain stress; and thereafter forming a second embedded epitaxial layer in the substrate adjacent to the second dummy gate structure.
 2. The method for fabricating a metal-gate CMOS device according to claim 1 further comprising: forming a first dielectric layer on the first CESL; performing a chemical mechanical polishing (CMP) process to remove a portion of the first dielectric layer and a portion of the first CESL to expose the first and second dummy gate structures; removing the first and second dummy gate structures to thereby form a first gate trench and a second gate trench; and forming a first gate dielectric layer and a first metal gate in the first gate trench, and forming a second dielectric layer and a second metal gate in the second gate trench.
 3. The method for fabricating a metal-gate CMOS device according to claim 1 wherein the first region is PMOS region and the second region is NMOS region.
 4. The method for fabricating a metal-gate CMOS device according to claim 1 wherein the first spacer comprises carbon-doped silicon nitride.
 5. The method for fabricating a metal-gate CMOS device according to claim 1 wherein the second spacer comprises carbon-doped silicon nitride.
 6. The method for fabricating a metal-gate CMOS device according to claim 1 wherein the seal layer is a silicon nitride seal layer.
 7. The method for fabricating a metal-gate CMOS device according to claim 1 wherein the first embedded epitaxial layer is in-situ doped with a first conductivity dopants and the second embedded epitaxial layer is in-situ doped with a second conductivity dopants.
 8. The method for fabricating a metal-gate CMOS device according to claim 7 wherein the first conductivity dopants are P type dopants and the second conductivity dopants are N type dopants.
 9. The method for fabricating a metal-gate CMOS device according to claim 2 further comprising: removing the first dielectric layer, the first CESL and the seal layer; depositing a stressed second CESL; forming a third dielectric layer on the stressed second CESL; etching the third dielectric layer and the stressed second CESL in the first region to form a first contact hole, and etching the third dielectric layer and the stressed second CESL in the second region to form a second contact hole; forming a silicide layer at a bottom of each of the first and second contact holes; and filling the first and second contact holes with a metal layer to thereby form a first contact plug and a second contact plug.
 10. The method for fabricating a metal-gate CMOS device according to claim 9 further comprising: forming a second dielectric layer on the substrate; etching the first and second dielectric layers, the first CESL and the seal layer in the first region to form a first contact hole, and etching the first and second dielectric layers and the first CESL in the second region to form a second contact hole; and forming a silicide layer at a bottom of each of the first and second contact holes; and filling the first and second contact holes with a metal layer to thereby form a first contact plug and a second contact plug. 